1. Field of the Invention
The present invention relates to a method of cleaning a film deposition apparatus or a vacuum processing apparatus, a method of dry etching such an apparatus, and an article production method including a process based on the cleaning or dry etching method. More particularly, the present invention relates to a method of cleaning a film deposition apparatus or a vacuum processing apparatus for forming a deposition film on a substrate to produce an electrophotographic photoreceptor or a semiconductor device such as a solar cell, a line sensor for inputting an image, an imaging device, or a TFT, a method of dry etching such an apparatus, and an article production method including a process based on either one of such methods.
2. Description of the Related Art
Various deposition films have been proposed for use in an electrophotographic photoreceptor and a semiconductor device such as a solar cell, a line sensor for inputting an image, an imaging device, and a TFT. An example is a film of amorphous silicon such as that compensated with hydrogen and/or halogen (such as fluorine or chlorine) (hereinafter referred to as xe2x80x9ca-Si(H, X)xe2x80x9d). Some of them are practically used. Various apparatuses and methods for depositing a film such as a-Si(H, X) are known. Specific examples of film deposition methods include vacuum evaporation, ion plating, sputtering, thermal CVD, plasma CVD, and optical CVD. Of these film deposition methods, a low-pressure method such as plasma CVD is widely used.
When a deposition film is formed on a desired substrate using one of the above methods, the film or a polymer (polysilane) in the form of particles is also deposited on some parts of a film deposition chamber. For example, when a deposition film is formed by means of the plasma CVD method using glow discharge decomposition, the deposition film is formed not only on the substrate but also on various parts other than the substrate, such as the susceptor and the opposite electrode, in the film deposition apparatus (hereinafter also referred to as a xe2x80x9creactor chamberxe2x80x9d) and on the inner wall of the reactor chamber. The deposition film or polysilane is incorporated as an impurity into a film formed in the next deposition process. Such incorporation of an impurity can cause degradation of the quality of the film. Polysilane deposited on the substrate can cause the film to have a defect. As the film deposition process is repeated, the production yield greatly decreases.
One known technique to avoid the above problem is to clean the inside of the reactor chamber every one or more film deposition cycles to remove the film or polysilane deposited on parts other than where the film should be deposited. One known cleaning method is to use a chemical vapor reaction to reduce the deposited film or elements forming polysilane by means of vapor molecules. In this cleaning method, a gas such as CF4, NF3, or SF6 is used as a cleaning gas and is supplied into the reactor chamber. The cleaning gas supplied into the reactor chamber is excited by energy of plasma, heat, or light so that the gas in the excited state reacts with elements forming the deposited film or particles, thereby converting them into vapor molecules, which are then removed by vacuum pumping means.
In recent years, ClF3 has attracted large attention as an etching gas. ClF3 is decomposed by low energy and is very active. The etching rate of ClF3 is extremely high compared with the etching rates of conventional etching gases.
Various cleaning methods by means of dry etching using ClF3 have been proposed. For example, Japanese Patent No. 2720966 discloses a cleaning method using a gas containing at least one of ClF, ClF3, and ClF5. Those methods using ClF3 allow the cleaning to be performed in a highly efficient manner.
In recent years, there has been a need for a further improvement in image quality of electrophotographic apparatuses. In order to meet the above requirement, the resolution of developing a latent image on an electrophotographic photoreceptor has been increasingly improved.
An increase in the speed of copying machines has been also achieved. As a result, the charging process has become critical, that is, charging is needed to be performed in a shorter time. This produces a problem that when no voltage is applied to a certain portion of the surface of the photoreceptor, that portion can have a large influence upon the voltage in neighboring portions, and thus an image defect is produced in that portion.
In conventional electrophotographic apparatuses, the main purpose is to make a copy (line copy) of a document including only character information, and thus an image defect does not practically result in a significant problem. However, in recent more sophisticated copying apparatuses, it is needed to make a high-quality copy of a document including halftone information such as a picture, and an image defect which is not a significant problem in a line copy can result in a significant problem. As a result, an electrophotographic photoreceptor containing a lesser number of defects is needed for use in an electrophotographic photosensitive drum. In particular, in a certain type of electrophotographic copying machine, an image defect is visually prominent, and thus the electrophotographic photosensitive drum needs to includes a still smaller number of defects.
Thus, there has arisen a need to effectively produce an electrophotographic photoreceptor having extremely high quality with a high production yield.
However, the above-described conventional cleaning techniques for removing the undesired deposition film or polysilane remaining in the reactor chamber after forming the desired deposition film have the following problems to be solved to meet the requirements in terms of the characteristics of the articles such as a photoreceptor (photosensitive drum with a very large size).
That is, in the conventional techniques in which polysilane is removed by reacting polysilane with ClF3 gas, the cleaning process needs a long time to remove polysilane to a sufficient degree, and thus it is needed to supply a large amount of ClF3 and a large amount of electric power. Furthermore, the vacuum pumping means, in particular, the rotary pump, needs to continuously suck ClF3 gas for a long time, and a large load is imposed upon the vacuum pumping means. If the removal of polysilane is not sufficient, particles remain mainly on the inner wall of the reactor chamber. It is known that the remaining particles can fly off during a subsequent film deposition process and can form defects in a deposited film.
When a large-sized product which is long in one direction (as with an electrophotographic photosensitive drum) is produced, the remaining deposition film or polysilane is nonuniformly distributed in the reactor chamber, and thus the cleaning process can become nonuniform. This can cause insufficient removal of polysilane and thus can cause the produced electrophotographic photosensitive drum to have a small image defect. Although the size and the density of defects are sufficiently low for use in conventional applications, the defects cannot be neglected in recent sophisticated apparatuses in which high resolution and high image quality are required.
It is an object of the present invention to provide methods of cleaning and dry etching a film deposition apparatus, capable of effectively removing by-products from the inside of a reactor chamber, sufficiently to make it possible to form high-quality deposition films, and in particular, high-quality electrophotographic photosensitive drums, at a satisfactory speed.
One aspect of the present invention is a method of cleaning a film deposition apparatus for depositing a film on a substrate placed in a reactor chamber which can be evacuated to a low pressure, wherein the cleaning is performed by applying a cleaning gas and high-frequency power, and in which the application of high-frequency power is temporarily stopped in the middle of the cleaning process and then restarted.
Another aspect of the present invention is a method of dry etching a vacuum processing apparatus, including first, second and third dry etching steps. In the first dry etching step, high-frequency power and a dry etching gas are supplied under a low pressure, thereby dry etching an undesired solid substance present in the vacuum processing apparatus. In the second dry etching step, the first dry etching step is stopped by stopping the supplying of the high-frequency power and the dry etching gas, and the undesired solid substance is then further dry etched while the power and gas are no longer being supplied (i.e., during the stopping of the first dry etching step). In the third dry etching step, the second dry etching step is terminated by resuming supplying of the high-frequency power and the dry etching gas, and the undesired solid substance is dry etched. Still another aspect of the present invention is a method of producing an article, including a film depositing step, in which a substrate is placed in a reactor chamber and a film is deposited on the substrate, and a cleaning step. The cleaning step includes three cleaning steps, in the first of which, after completion of the film depositing step, the substrate is taken out of the reactor chamber, and a cleaning gas and high-frequency power are supplied into the reactor chamber. In the second cleaning step, the supplying the cleaning gas and of the high-frequency power is stopped, and in the third cleaning step, the cleaning gas and the high-frequency power are supplied again. After completion of the cleaning step, the film depositing step can be performed again to deposit a film on another substrate.
In various aspects of the present invention, the supplying of the cleaning gas and the high-frequency power is temporarily stopped during the cleaning process so that a moderate reaction occurs between the cleaning gas remaining in the film deposition apparatus and the undesired solid substance (such as the undesired deposition film or polysilane), whereby the undesired substance is further removed under reduced pressure without being intentionally subjected to factors or conditions which would enhance the reaction. Thereafter, the cleaning process is restarted. This method allows the cleaning process to occur in an efficient manner and makes it possible to uniformly form a high-quality deposition film, in particular, a high-quality electrophotographic photosensitive drum (electrophotographic photoreceptor) with good repeatability.
In the present specification, the term xe2x80x9ccleaning processxe2x80x9d refers to a process including the steps of to supplying a cleaning gas into a reactor chamber of a film deposition apparatus and supplying electric power into the reactor chamber in which the cleaning gas is being supplied. In various aspects of the present invention, the cleaning process preferably further includes the step of stopping supplying the high-frequency power in the middle of the cleaning process and more preferably stopping supplying both the cleaning gas and the high-frequency power. The supplying of the high-frequency power is not necessarily stopped completely; rather, the high-frequency power can merely be substantially stopped by reducing the high-frequency power to a low enough level to generate substantially no discharge.
From another point of view, the cleaning process according to various aspects of the present invention can be regarded as having two cleaning steps, before and after a period during which the supplying of the high-frequency power is stopped or the supplying of both the high-frequency power and the cleaning gas is stopped, wherein, in each of the two cleaning steps, the cleaning gas is supplied into the reactor chamber of the film deposition apparatus and the high-frequency power is supplied into the reactor chamber into which the cleaning gas is being supplied.
In the present specification, the reaction which occurs in the period between the two cleaning steps is referred to as the xe2x80x9cmoderate reactionxe2x80x9d. In this moderate reaction, cleaning is also performed, that is, the undesired substance is dry etched.
In the two cleaning steps before and after the moderate reaction period, the etching gas serving as the cleaning gas is supplied into the reactor chamber and the high-frequency power is also supplied into the reactor chamber thereby actively removing the undesired substance. In the moderate reaction period, because the high-frequency power is not supplied into the reactor chamber, or the high-frequency power and the cleaning gas are not supplied, the undesired substance is removed under the reduced pressure in a moderate manner in which no active reaction occurs.
The conditions of supplying the high-frequency power, that is, the frequency and the magnitude of the high-frequency power, may be the same or may be different for the two cleaning steps, i.e., before and after the moderate reaction period. Employing the same conditions is more desirable in that the cleaning process can be performed in a short time using a simple process.
Furthermore, the type of the cleaning gas (dry etching gas) and the flow rate of the cleaning gas (dry etching gas) may be the same or may be different for the respective two cleaning steps (before and after the moderate reaction period). Employing the same type of gas and the same flow rate is more desirable in that the cleaning process can be performed in a short time using a simple process.
The present invention is based upon the following knowledge obtained through an investigation performed by the inventors of the present invention. That is, the inventors expected at an early stage of their investigation that undesired solid substances such as a deposition film or polysilane remaining in the reactor chamber after completion of the film deposition process could be removed by reacting the undesired solid substances with the cleaning gas activated by discharging energy. However, in reality, the cleaning process occurs nonuniformly and the nonuniformity causes residual particles still to remain on the inner wall of the reactor chamber even after the cleaning process. In order to remove the particles perfectly, it is needed to perform the cleaning for a long time, and thus a large amount of cleaning gas and a large amount of electric power are consumed.
The inventors have attempted to remove the particles perfectly by increasing the concentration of the cleaning gas. However, it turned out that a simple increase in the concentration resulted in an increase in the amount of residual particles because of reaction between the cleaning gas and the residual deposition film or particles. That is, a simple increase in the concentration of the cleaning gas resulted in an adverse effect.
The inventors have also attempted to decrease the concentration of the cleaning gas. When the concentration of the cleaning gas was simply reduced, although a moderate reaction was obtained, a reduction in the cleaning speed occurred also, and thus a simple reduction in the concentration of the cleaning gas is not practical. Thus, either a simple increase or reduction in the concentration cannot solve the problem of nonuniformity in cleaning.
The inventors have made a further investigation and have developed an excellent method in which supplying a cleaning gas and high-frequency power into the reactor chamber is temporarily stopped during the cleaning process and is restarted after the temporary stoppage.
During the period in which the supplying of the cleaning gas and the high-frequency power is temporarily stopped, a moderate cleaning process is performed by the cleaning gas remaining in the reactor chamber. This moderate cleaning process allows a reduction in the cleaning nonuniformity and also makes it possible to remove, in a short time, particles which would otherwise remain in the reactor chamber.
It has been found that the cleaning effect can be enhanced by restarting the cleaning process at a different concentration of the cleaning gas. This allows a reduction in the total cleaning time.
The article production method according to the present invention allows the reactor chamber to be cleaned in a highly efficient manner between adjacent two film deposition cycles, making it possible to produce high-quality articles with good reproducibility at low cost.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments.